The globalization of ideas via the Internet, air travel, and migration is profoundly affecting the world. In once-isolated communities, exposure to the new and different can prompt a reaction of anger, fear, even terrorism. But the tide of freedom and human dignity is immensely more powerful -- and ultimately unstoppable.

Ecology describes the balance of living things and their habitat – a colony of birch trees, an anthill, a city, a civilization. When the balance is broken by overpopulation, disease, resource depletion, migration, technology, or the wildfire of fads and fears, conflicts can occur. So can something else. Ideas combine and recombine when they come into contact. Food, fashion, business, and art fuse. Old cultures evolve. New ones are born.

The story of the late 20th and early 21st centuries is how globalization has massively upset the ecological order. Pockets of humanity that once seemed remote are now connected – for better most of the time, but sometimes for worse.

The Monitor office is located at 42° North, 71° West in a pleasant North American neighborhood peopled by everyone from seniors to transients, multi-pierced music students to pinstriped lawyers. An easy lunchtime stroll away is Boylston Street, where on April 15 a cruel act of terrorism disrupted a happy holiday gathering at the end of an egalitarian footrace.

The older of the brothers charged with carrying out the attacks – Chechen by way of Kyrgyzstan and Dagestan but largely raised in the Boston area, married to an American, and so, really, almost quintessentially a product of the American melting pot – is said to have nursed grievances about the wars in Iraq and Afghanistan, though he had no personal or family ties to those conflicts. Why he thought killing and maiming the innocent on a Boston street would redress those grievances will never be understandable.

The pain inflicted and the tears shed will not soon be forgotten. But consider what we discovered about ourselves. Instead of anger or fear something different broke out: resolve. This is the world we live in, millions of people seemed to decide all at once. We won’t accept evil, nor will we fear it. And we won’t diminish the good. In fact, we’ll amplify it through support and charity, through cooperation with one another, and by holding firm.

If there ever was a time of splendid isolation – and that may be more rose-colored hindsight than reality – that is not today. A plane ticket or the click of a mouse puts us in contact with almost anyone anywhere on the planet. Ideas and arguments, friendships and disputes, flow freely. Millions of eyes now see what just a few in the mainstream media used to see. That brings with it stereotype-breaking possibilities and the power of millions of thinkers in solving problems. It brings abundant intelligence but also mischief – and sometimes hatred.

The ecological order is always being upset. In another age, when the Roman world was in turmoil, Augustine of Hippo argued that we live in both the City of Man and the City of God. One is constantly in flux. The other is a spiritual constant.

In 2013, the unstoppable ideas of universal freedom and human dignity – embodied by, but not limited to, the American experience – have gone global. That thrills millions and upsets some, which makes the City of Man interesting and dangerous, liberating and threatening. Living in it requires the resolve we’ve seen in Boston, London, Madrid, Jerusalem, Mumbai, Bali, New York, and every other place attacked by freedom’s discontents.